In recent years, recording mediums are directed toward those having a much higher performance, and there is a demand for the advent of magnetic disks and magnetic tapes having electromagnetic conversion characteristics high enough to enable high-density recording.
In order to improve electromagnetic conversion characteristics of magnetic recording mediums, various attempts have been hitherto made, e.g., attempts to use magnetic powders having a high saturation magnetization, to make particles of magnetic powder finer and improve the dispersibility that comes into question as a result thereof, and, with regard to magnetic layers, to use a multi-layer system, to improve squareness ratio, coercive force and saturation flux density, and also to control surface smoothness.
In the attempt to make particles of magnetic powder finer, it has become popular to use, for example, a ferromagnetic metal powder with fine particles which are made increasingly finer as magnetic tapes of an 8 mm type such as a high-band 8 mm system are made to have a higher image quality.
However, as particles are made finer as stated above, magnetic tapes may cause, e.g., the following problems:
1) Edge damage that is caused by a decrease in Young's modulus, and a poor running durability due to the sticking of tape. PA0 2) Chroma output drop. PA0 3) A poor transfer performance. PA0 4) A lowering of detectability at the tape end because of an increase in light transmittance. PA0 5) Output drop after tape running under low humidity (40.degree. C., 20%).
Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 19524/1989 discloses a technique in which a ferromagnetic metal powder with an average major axis length of less than 0.25 .mu.m and a crystallite size of less than 200 .ANG. is used in the outermost layer and a ferromagnetic metal powder with an average major axis length of not less than 0.25 .mu.m and a crystallite size of not less than 250 .ANG. is used in a layer other than the outermost layer.
The above technique can overcome the problems 3) and 4) to a certain extent, but still has had problems regarding the poor running durability in the item 1), the chroma output drop in the item 2) and the output drop after tape running under low humidity (40.degree. C., 20%) in the item 5). In addition, in this technique, a magnetic powder with an average major axis length of not less than 0.25 .mu.m and a crystallite size of not less than 250 .ANG., which is relatively large in size, is used in a layer other than the outermost layer so that transfer performance and light screening properties of tapes can be improved, and hence has had the disadvantage that the surface properties of a lower layer become poor to make large the surface roughness of the outermost magnetic layer, rather resulting in a lowering of electromagnetic conversion characteristics.
As for the drop of chroma output stated above, Japanese Patent O.P.I. Publications No. 53022/1992 and No. 61023/1992 each disclose an improved technique to solve the problem, but can not be said to be a satisfactory improvement from the viewpoint of practical use.